Moveable devices are used downhole to perform a number of functions. These devices may include, for example, chokes, sliding sleeves, and other valves. Sliding sleeve valves are used downhole to control and regulate fluids flow through tubulars. Controlling fluid flow is important for various economic reasons. For example, sliding sleeves can be used to shut off zones producing too much water or depleting hydrocarbons produced by other zones. Typically, sliding sleeve valves consist of an external housing that is threaded to the tubing string. The housing has openings, known as flow ports, to allow fluid flow into or out of the tubing. Inside the housing, there is a sliding sleeve, known as the insert, whose axial position with respect to the housing is adjustable to open or close the flow ports.
Sliding sleeves are either mechanically or hydraulically actuated. Mechanical actuation involves using a lock that is run in the well on a wireline, coiled tubing or slickline tool. The lock engages onto a nipple in the sliding sleeve, and is then used to adjust the position of the sleeve. Hydraulic actuation involves using a hydraulic pump at the surface and more complicated actuation mechanisms.
In all cases, it is highly desirable to detect the operational condition of the sleeve (open/closed/partially open) after actuation. Historically, this was done by mechanically sensing the gap between the endpoint of the insert and the housing. Such mechanical detection involves using deployable arms and in contact measurements. It can, therefore, be unreliable and difficult to interpret in many cases.
Methods to detect the position of sliding sleeves using magnets and wireline or memory tools were disclosed in U.S. Patent App. Publication No. 2008/0236819 (Foster et al.), entitled “Position sensor for determining operational condition of downhole tool”, and U.S. Pat. No. 7,810,564 (Montgomery et al.), entitled “Memory logging system for determining the condition of a sliding sleeve.” These methods involve disposing magnets in predetermined positions along the sliding sleeve housing and insert, and using a magnetic field detection tool, such as casing collar locator, to detect the relative position between these magnets, from which the operational condition of the sleeve is inferred. Another method was disclosed in U.S. Pat. No. 7,000,698 (Mayeu et al.), entitled “Methods and systems for optical endpoint detection of a sliding sleeve valve,” whereby fiber optic based sensors where utilized for endpoint detection of sliding sleeves. The optical sensors are positioned in a recess in the valve housing, and are used to detect the stress imparted by the moving sleeve.
The drawback of all the above methods is that they only work for customized sliding sleeves equipped with magnets or optical sensors. This increases the cost and complexity of the sliding sleeves in new deployments, and makes the detection methods unusable for existing deployments having conventional sleeves.